We are looking at stringing single mode fibre
from utility poles halfway up a mountain in the
Canadian Rocky mountains to connect two buildings.
We would use figure eight cable (integrated
messenger).

Temperatures vary from +80 F (about 30C) in
summer to -40F (about -35C) in winter. Colder
than this is uncommon but does happen.

Most fibre I've seen is spec'd down to
-40F.

What happens to fibre when it gets too cold?
And how cold is too cold?

Thanks in advance!

Eric